Diaphragm

The diaphragm is a large, dome-shaped skeletal muscle that separates the thoracic cavity from the abdominal cavity. It is the primary muscle of inspiration (inhalation). When it contracts, it flattens, increasing thoracic volume and decreasing intra-thoracic pressure, drawing air into the lungs. It is controlled by the phrenic nerves (C3-C5) and also aids in defecation, urination, and childbirth.